Question

Which of the following statements about eutrophication are correct?

(i) It can be a naturally occurring process.

(ii) It commonly occurs in stagnant rather than running water.

(iii) It does not affect oxygen level of water bodies.

(iv) It is commonly associated with high levels of phosphates and nitrates.

• A. i, ii and iv
• B. i, ii and iii
• C. ii, iii and iv
• D. all of these

Answer 1

The correct option is A i, ii and iv

Eutrophication is the process of natural aging of a lake due to the enrichment of nutrients in its water. In a young lake, water used to be very cold, clear and supported minimal life. The water from connecting streams that drained into the lake, with time, introduced nutrients such as nitrogen and phosphorus.

Addition of nitrogen and phosphates helps in the enormous growth of aquatic organisms and thereby increases the fertility of the lake. Plant and animal life flourishes and results in the deposition of organic remains at the lake bottom. As organic debris piles up, the lake became shallower and warmer. The warm-water favours the growth of organisms that survived in warm environments and replaces those in cold environments. Marsh plants begin to fill in the original lake basin. Eventually, the lake gets filled with large masses of floating plants (bog), finally converting into land.